For n>=4 a(n)=2^4=16. This sequence is the transform of A115291 by the following transform T: T(u_0,u_1,u_2,u_3,u_4,...)=(u_0,u_0+u_1, u_1+u_2,u_2+u_3,aso); we observe that T(A040000)=A113311 and also T(A113311)=A115291...